GB2140331A

GB2140331A - Development of electrostatic images

Info

Publication number: GB2140331A
Application number: GB08413057A
Authority: GB
Inventors: Yoshio Miyauchi; Kiyosi Takenaka; Yoshihiko Bessho
Original assignee: Dainippon Screen Manufacturing Co Ltd
Current assignee: Dainippon Screen Manufacturing Co Ltd
Priority date: 1983-05-26
Filing date: 1984-05-22
Publication date: 1984-11-28
Also published as: GB8413057D0; DE3419053A1; FR2546641B1; FR2546641A1; JPS59184152U; JPH0339796Y2; GB2140331B; DE3419053C2; US4586809A

Description

1 GB 2 140331 A 1

SPECIFICATION

Development of electrostatic images THIS INVENTION relates to development of 70 electrostatic images.

In order to develop electrostatic latent im ages formed on electro-photographic photore ceptors (hereinafter referred to as "photosen sitive substrates") using the developing appa ratus of an electrophotographic copying ma chine, a developing process wherein the pho tosensitive substrate is advanced smoothly and an even and adequate developing of the photosensitive substrate with the rear surface of the substrate free from any toner staining is ordinarily indispensable if clear duplicate im ages are to be produced.

Different types of liquid developing appara tus have been proposed in order to meet the above requirements. The liquid developing apparatus disclosed in Japanese Patent Appli cation laid open under provisional publication No. Sho 49-62148, for example, is one of the most desirable types. However, the struc ture of the apparatus described therein is both intricate and complicated and the manufactur ing costs are comparatively high.

It is, therefore, an object of the present invention to provide developing apparatus suitable for use in an electrophotographic copying machine which eliminates or at least mitigates the above mentioned disadvantages and which is, comparitively, of simple con struction and for which manufacturing and maintenance are easier.

According to the present invention there is provided developing apparatus suitable for use in an electrophotographic copying ma chine for transferring a photosensitive sub strate carrying a latent image on one surface thereof along a path provided between op posed electrode plates, the apparatus compris ing a developing solution discharge outlet for supplying developing solution to develop the latent image on the one surface of a photo sensitive substrate being transferred along the path and a developing solution storage tank for supplying developing solution to the other surface of a photosensitive substrate being transferred along the path.

In a second aspect, the present invention provides developing apparatus suitable for use in an electrophotographic copying machine for transferring photosensitive substrate along a flow path for developing solution provided between opposed electrode plates, the appara tus comprising a developing solution storage tank upstream of the path and a developing solution discharge outlet positioned so as to face a latent image surface of a photosensitive substrate when, in use of the apparatus, the substrate is transferred along the path.

Preferably, a developing solution feeder is provided to fill the path between the electrode 130 plates with developing solution supplied from the developing solution discharge outlet and to fill the solution storage tank. Usually means are provided for returning developing solution transferred along the path to the developing solution feeder. Conveniently the return means comprises a circulating pump. Generally the solution storage tank is arranged to contain sufficient developing solution required by at least one photosensitive substrate when the major portion of the developing solution in the storage tank flows down under gravity along the other surface of the photosensitive substrate.

In a preferred arrangement, the developing solution storage tank is disposed to supply developing solution to the path from the side thereof defined by one of the electrode plates and the developing solution discharge outlet is disposed to supply developing solution to the path from the side thereof defined by the other of the electrode plates and, normally, the surface of the other electrode plate facing the one electrode plate comprises a fluori- nated resin or polymer having a low coefficient of friction. Preferably, the fluorinated resin or polymer is polytetrafluorethylene.

Generally, the surface of the other electrode plate facing the one electrode plate is uneven or grained to provide, in use, a low contact point density with a photosensitive substrate being transferred along the path.

In a further aspect, the present invention provides a method of developing a latent image carried on one surface of a photosensitive substrate, comprising transferring a photosensitive substrate along a path provided between opposed electrode plates, supplying developing solution from a developing solu- tion discharge outlet to the one surface of the photosensitive substrate being transferred along the path to develop the latent image thereon and supplying developing solution from a developing solution storage tank to the other surface of the photosensitive substrate being transferred along the path to facilitate smooth transfer of the photosensitive substrate along the path.

Preferably, the developing solution is sup- plied to the path between the electrode plates via the developing solution discharge outlet prior to transfer of a photosensitive substrate along the path to fill the developing solution storage tank which, when the photosensitive substrate is transferred along the path, supplies developing solution to the other surface thereof, the discharge outlet supplying developing solution to the one surface carrying the latent image. Normally, unused developing solution transferred along the path is returned along a return path to the developing solution discharge outlet and the storage tank.

For a better understanding of the present invention, and to show how the same may be put into effect, reference will now be made, 2 GB 2 140331 A 2 by way of example, to the accompanying drawing, in which:

Figures 1 and 2 are side cr6ss-sectional views of previous liquid developing apparatus; Figure 3 is a cross-sectional view of liquid developing apparatus in accordance with the present invention; Figure 4 is a cross-sectional view of part of the apparatus of Fig. 3 showing the surface of an auxiliary electrode plate thereof; and Figure 5 is a side cross-sectional view of an alternative embodiment of liquid developing apparatus in accordance with the invention.

Referring now to the drawing, Fig. 1 is a cross-sectional view of liquid developing appa- 80 ratus for an electrophotographic copying ma chine, that is a photocopying machine, such as that disclosed in Japanese Utility Model Application published under publication No.

56-14525, wherein a photosensitive sheet or 85 substrate 1 having an electrostatic latent im age thereon is transferred in the direction of the arrow by feed rollers 2 and 3 and is passed between a tilted main electrode plate 4 and an auxiliary electrode plate 5 facing the main electrode plate. At this time, developing solution is supplied to a solution feeder 6 by a pump (not shown) and is forcibly supplied between the main and auxiliary electrode plates 4 and 5 in an even flow from a slit shaped discharge outlet 7.

Thus, the photosensitive sheet 1 is devel oped while the sheet I passes between the opposed electrode plates 4 and 5 so that the electrostatic latent image is turned into a visible image. The developed photosensitive sheet 1 is passed out of the developing equip ment via squeeze rollers 8 and 9 which re move excess developing solution from the developed photosensitive sheet.

The above-described developing apparatus is one of the most popular types. If the electrostatic latent image is positioned upper most as seen in the Figures, the arrangement shown in Fig. 1 is used while if the image is disposed on the underneath side of the photo sensitive sheet, the inverted arrangement shown in Fig. 2 is used.

The following conditions are generaly consi dered to be necessary if clear duplicated cop ies are to be obtained. Thus, to obtain even and adequate developing results, the spacings between the main electrode plate 4, the pho tosensitive sheet 1 and the auxiliary electrode plate 5 should be even and the spacing 120 between the opposing electrode plates 4 and should be adequate. Also to prevent the rear surface of the photosensitive sheet 1 being stained by toner and to avoid random electric charges occuring on the photosensi tive sheet, the rear surface of the photosensi tive sheet should not be placed in contact with the auxiliary electrode plate 5. Further, a guide having a low friction resistance is neces sary to ensure the smooth advance of the 130 photosensitive sheet through the processing apparatus.

A number of attempts have been made to comply with the above-mentioned require- ments. Thus, Japanese Patent Application laid open under Provisional Publication No. 49-62148, for example, describes liquid developing apparatus wherein developing solution is applied to both sides of the photosensitive sheet 1 and a nylon thread having a higher electric resistance than the developing solution is stretched to face the auxiliary electrode plate. The photosensitive sheet 1 is positioned using the nylon thread as the guide so as to meet the above-mentioned conditions or requirements. This equipment has, however, disadvantages in that the structure is complicated and intricate and the manufacturing costs are comparitively high. Japanese Utility Model Application published under Publication No. 56-14525 describes developing equipment wherein electro-conductive mesh is stretched opposite to the auxiliary electrode plate 5 to provide the necessary guide to position the photosensitive sheet. In tests, however, the electro-conductive mesh is found to have some disadvantageous effects, one of which is that the positive polarization charge on the back of the photosensitive sheet 1 is lost by the electro-conductivity of the mesh and the negative charge on the corresponding latent image surface is reduced, so lowering toner deposition by Coulomb's force and making it impossible to obtain adequate developing results. Another disadvantage is that staining of the back or rear surface of the photosensitive sheet cannot be prevented even by using a fine mesh of about #300, for example. Another disadvantage is that with repeated use the toner sticks to the mesh and can hardly be removed when dry. Moreover, particularly with the first copy of the day, the rear surface is stained by the partial unevenness of image density and by physical con- tact. If an adequate amount of developing solution is not passed between the photosensitive sheet 1 and the auxiliary sheet electrode plate 5, in particular, these disadvantages are significant.

Fig. 3 is a sectional view of liquid developing apparatus embodying the invention. It should be understood that in Figs. 1 to 5 components having the same function are designated by the same reference numerals.

As is clear from Figs. 1 to 3, the apparatus of Fig. 3 differs from that shown in Figs. 1 and 2 by, inter alia, the fact that a solution tank 10 is placed upstream of the developing solution flow channel or path formed by the tilted and opposed electrode plates 4 and 5.

The operation and action of the apparatus of Fig. 3 will now be described.

Developing solution supplied to the solution feeder 6 by a pump (not shown), prior to the feeding of the photosensitive sheet 1 between 3 GB 2 140 33 1 A 3 the plates 4 and 5, passes through the slit shaped discharge outlet 7 crossing the flow channel so as to be forcibly injected into the channel in an even and smooth flow. After the flow channel has been filled, the injected 70 solution is stored in the upstream solution tank 10. A photosensitive sheet 1 is then conveyed in the direction of the arrow in Fig.

3 by the feed rollers 2 and 3 with the latent image surface thereof facing downwardly, that is, facing the main electrode plate 4. By means of the guide 1, the top surface of the photosensitive sheet 1 is first passed into the solution tank 10 and then up to the flow channel. At this time, the photosensitive sheet 80 1 is pushed up against the side of the aux iliary electrode plate 5 by the developing solution ejected from the discharge outlet 7 and is carried along the auxiliary electrode plate 5 as illustrated in Fig. 4.

The developing solution tank 10 flows down naturally between the rear surface of the photosensitive sheet 1 and a grained or uneven surface 12 of the auxiliary electrode plate 5 to be used up almost completely. The developing solution naturally flowing down at this time has the effect of providing a liquid bearing which reduces the friction and resis tance between the grained surface 12 and the rear surface of the photosensitive sheet 1 to almost zero so promoting smooth advance of the photosensitive sheet. The capacity of the solution tank 10 should be large enough, at least, to enable the tank to contain or store the developing solution used up by a sheet of photoreceptor that is the sheet of photosensi tive material 1.

The developing solution flowing down from upstream and downstream of the developing apparatus is recovered in a tray (not illus trated) and is returned to the developing solu tion feeder 6 by a circulation pump (not shown). The rate of flow, that is the quantity of developing solution discharged from the developing solution feeder 6 connected to the circulation pump is arranged to be sufficient to fill the flow channel and also to fill the solution tank rather quickly.

The latent image on the photosensitive sheet 1 is turned into a visible image in the flow channel by the toner in the developing solution forcibly injected into the flow channel via the discharge outlet 7 and the developed photosensitive sheet, passes out of the devel oping equipment by the squeeze rollers 8 and 9.

The surface of the auxiliary electrode plate is formed (by sand blasting, for example) into a grained or uneven surface having a low contact point density at the contact with the back side of the photosensitive sheet and is covered with a fluorinated resin or polymer having a low coefficient of friction (for example polytetrafluoroethylene which is sold under the name TEFLON (Registered Trade Mark)) and which is an electronically resistive material free from charge or electification. The photosensitive sheet 1 transferred along the grained surface 12 thus advances smoothly and the rear surfa6e is free from staining. Developing apparatus embodying the invention having a solution tank upstream of the flow channel formed between the tilted and opposed electrode plates and upstream of the slit shaped solution discharge outlet 7 which is positioned facing to the latent image surface of the photosensitive sheet has the effect of providing a liquid bearing for smooth transfer of the photosensitive image in addtion to the effect of the grained surface between the auxiliary electrode plate and the photosensitive sheet under natural flow, that is flow under gravity, of the developing solution. It should however be noted that it would also be acceptable to use a nylon material as employed by previous apparatus in place of the grained or uneven surface 12. Thus, the construction of apparatus embodying the invention and the manufacturing and maintenance are easier than with the previous apparatus in which developing solution is forced to pass through both sides of the photosensitive sheet 1.

Claims

1. Developing apparatus suitable for use in an electrophotographic copying machine for transferring a photosensitive substrate carrying a latent image on one surface thereof along a path provided between opposed electrode plates, the apparatus comprising a developing solution discharge outlet for supplying developing solution to develop the latent image on the one surface of a photosensitive substrate being transferred along the path and a developing solution storage tank for supplying developing solution to the other surface of a photosensitive substrate being transferred along the path.

2. Developing apparatus suitable for use in a electrophotographic copying machine for transferring photosensitive substrate along a flow path for developing solution provided between opposed electrode plates, the apparatus comprising a developing solution tank upstream of the path and a developing solution discharge outlet positioned so as to face a latent image surface of a photosensitive substrate when, in use of the apparatus, the substrate is transferred along the path.

3. Apparatus accoridng to claim 1 or 2 wherein a developing solution feeder is provided to fill the path between the electrode plates with developing solution supplied from the developing solution discharge outlet and to fill the solution storage tank.

4. Apparatus according to Claim 3, wherein means are provided for returning developing solution transferred along the path to the developing solution feeder.

4 GB 2 140 331 A 4

5. Apparatus according to Claim 4, wherein the return means comprises a circulating pump.

6. Apparatus according to any preceding claim, wherein the solution storage tank is arranged to contain sufficient developing solution required by at least by one photosensitive substrate when a major portion of the developing solution in the storage tank flows down under gravity along the other surface of the photosensitive substrate.

7. Apparatus according to any preceding claim, wherein the developing situation storage tank is disposed to supply developing solution to the path from the side thereof defined by one of the electrode paths and the developing solution discharge outlet is disposed to supply developing solution to the path from the side thereof defined by the other of the electrode plates.

8. Apparatus according to Claim 7, wherein surface of the other electrode plate facing the one electrode plate comprises a fluorinated resin or polymer having a low coefficient of friction.

9. Apparatus according to Claim 8, wherein, the flurinated resin or polymer is polytetrafluoroethylene.

10. Apparatus according to claim 7, 8 or 9, wherein the surface of the other electrode plate facing the one electrode plate is uneven or grained to provide, in use, a low contact point density with a photosensitive substrate being transferred along the path.

11. Developing apparatus suitable for use in an electrophotographic copying machine, substantially as hereinbefore described with reference to, and as illustrated in, Figs. 3 and 4 or Figs. 4 and 5 of the accompanying drawings.

12. A method of developing a latent image carried on one surface of a photosensitive substrate, comprising transferring a photosensitive substrate along a path provided between opposed electrode plates, supplying developing solution from a developing solution discharge outlet to the one surface of the photosensitive substrate beng transferred along the path to develop the latent image thereon and supplying developing solution from a developing solution storage tank to the other surface of the photosensitive substrate being transferred along the path to facilitate smooth transfer the photosensitive substrate along the path.

13. A method according to Claim 12 therein (13) the developing solution is supplied to the path between the electrode plates via the developing solution discharge outlet prior to transfer of a photosensitive substrate along the path to fill the developing solution storage tank which when the photosensitive substrate is transferred along the path supplies developing solution to the other surface thereof discharge outlet supplying developing solution to the one surface carrying the latent image.

14. A method according to Claim 13, wherein unused developing solution trans- ferred along the path is returned to the developing solution discharge outlet and the storage tank.

15. A method of developing a latent image carried on the surface of a photosensitive substrate substantially as hereinbefore described with reference to Figs. 3 and 4 or Figs. 4 and 5 of the accompanying drawing.

16. Any novel feature or combination of features described herein.

Printed in the United Kingdom for Her Majesty's Stationery Office. Dd 8818935. 1984. 4235 Published at The Patent Office, 25 Southampton Buildings. London, WC2A 1 AY, from which copies may be obtained z 4, A